1 Answer
1

Fullscreen API support was added in IE11, so IE9 and IE10 do not have the ability to make an Element full screen. Using IE9 or IE10, when MediaElement.js’ “Fullscreen” button is clicked, the script does a best-effort fallback by resizing the video to expand to the width/height of the window instead.

Disclosure: I am on the team that worked on Microsoft's implementation of the Fullscreen API.